Photoelectric detector for bobbin of a weaving loom

ABSTRACT

An improved photoelectric weft detector for fly-shuttle weaving looms utilizing photoelectric sensing means includes a first photocell positioned to sense specular and diffuse reflected light from a specified surface area of a bobbin, a second photocell positioned at approximately the same distance from the specified area of the bobbin to receive only diffuse reflected light and a third photocell mounted in proximity to the first photocell, which is adapted to receive both specular and diffuse reflected light and functions to inhibit the operation of the detector until the fly-shuttle is boxed. The photocells provide a voltage proportional to their resistance ratio for activiating a mechanism which replaces a bobbin upon exhaustion of the weft material. All of the photocells are provided with means for adjusting their distance to the specified area of the bobbin to increase their sensitivity to the light reflected therefrom.

[451 Dec. 4, 1973 PHOTOELECTRIC DETECTOR FOR BOBBIN OF A WEAVING LOOM [75] Inventor: Eugene A. Sansone, Belle Meade,

[73] Assignee: The Singer Company, New York,

22 Filed: Jan. 29, 1973 21 App]. No.1 327,338

Primary ExaminerWalter Stolwein AttorneyMarshall J. Breen et a].

[57] ABSTRACT An improved photoelectric weft detector for flyshuttle weaving looms utilizing photoelectric sensing means includes a first photocell positioned to sense specular and diffuse reflected light from a specified surface area of a bobbin, a second photocell positioned at approximately the same distance from the specified area of the bobbin to receive only diffuse reflected light and a third photocell mounted in proximity to the first photocell, which is adapted to receive both specular and diffuse reflected light and functions to inhibit the operation of the detector until the flyshuttle is boxed. The photocells provide a voltage proportional to their resistance ratio for activiating a mechanism which replaces a bobbin upon exhaustion of the weft material. All of the photocells are provided with means for adjusting their distance to the specified area of the bobbin to increase their sensitivity to the light reflected therefrom.

5 Claims, 3 Drawing Figures BACKGROUND OF THE INVENTION The present invention relates to weft detection systems and, more particularly, to a photoelectric detection system for detecting the exhaustion of material on a bobbin used in conjunction with a fly-shuttle weaving loom. Heretofore, weft detecting systems utilized mechanical sensing devices which were insensitive and wasted much of the weft material (yarn). These systems frequently frayed or tore the yarn due to the pressure exerted by the mechanical sensing device.

Prior art photoelectric sensing devices were also insensitive and frequently could not sufficiently distinguish between an empty or full bobbin in high ambient light. Frequently the bobbin was modified by providing a light reflecting surface or by providing two special surfaces, one highly reflective and the other nonreflecting, to increase the sensitivity and the reliability of the sensing device. However, modification or replacement of the existing bobbins in order to be able to utilize any of the prior art weft detecting systems is a costly added expense. Furthermore, photoelectric sensing systems known in the prior art did not provide or suggested means to enable the weft detecting apparatus to be calibrated or optimized for different looms. Frequently the performance had to be sacrified to enable a system to operate on a loom having dimensions different from that from which the detecting system was designed. Sudden changes or flashes in abient light would frequently activate the bobbin replacement mechanism before the weft had been expended from the bobbin.

SUMMARY OF THE INVENTION A prefered embodiment of the present invention does not require any modification of the bobbins presently in use, is reliably operable in high ambient light, is insensitive to sudden flashes of light which may occur during a major portion of the loom cycle, has a relatively high degree of sensitivity, and relies upon the inherent properties of the bobbins and the weft material themselves for operation.

An improved system for detecting in a specified area the presence or absence of material having afirst reflecting surface built in accordance with the principles of the present invention comprises; means having a second reflecting surface for supporting the material, means for providing light to the specified area, first means arranged to sense the light reflected from the specified area in the presence or absence of the material, the first means having an impedance proportional to the amount of light sense and being provided with means for adjusting the distance between the specified area and the first means to increase the sensitivity only to the light reflected therefrom, second means arranged only to sense light reflected from the specified area in the presence of the material, the second means having. an impedance proportional to the amount of light sensed, and being provided with means for adjusting the distance between the specified area and the second means to increase sensitivity only to light reflected therefrom, utilization means, third means coupled between the first and second means and the utilization means for activating the utilization means in accordance with a predetermined ratio of impedance of the first and second means responsibly to the presence or absence of the material, and fourth means coupled to the third means and mounted in close proximity to the first means, for activating the third means uponsensing light reflected by the absence of the material in the specified area. I

A complete understanding of the present invention may be obtained from the following detailed description, when taken in conjunction with the accompanying drawings in which:

DESCRIPTION OF THE DRAWING FIG. 1 is a front view in elevation of an embodiment of the present invention with the front cover removed showing the light paths with a full bobbin;

FIG. 2 is a front view in elevation of the apparatus of FIG. 1 showing the light path with an empty bobbin; and

FIG. 3 a schematic circuit diagram of a preferred embodiment of the photoelectric weft detector utilizing the principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and more specifically to FIGS. 1 and 2 wherein the numeral 10 represents a photoelectric weft detector system suitable for mounting on the main frame of a conventional fly-shuttle weaving loom having an automatic bobbin replacement mechanism. The operation of the loom is in no way altered by the present invention except that the automatic bobbin replacement mechanism is activated at the proper point of the loom cycle by a voltage obtained from a sensor utilizing the principles of the present invention.

A detailed explanation of the operation of a conventional fly-shuttle weaving loom is found in U.S. Pat. No. 3,373,773 granted Mar. 19, 1968 to George H. Balentine, Jr., Richard W. Johnson, and Thomas L. Cox. A further explanation of a photoelectric weft detector may be found in U.S. Pat. No. 3,693,671 granted Sept. 26, 1972 to Dhimat R. Desai.

Thephotoelectric weft detector system 10 includes several sub-assemblies, such as a control box 14 which houses the electronic circuitry for operation of the system, a systematic circuit diagramof which is shown in FIG. 3, a mounting bracket (not shown) for mounting to the main frame of a loom in juxtaposition to a shuttle box 20 which is located at each end of the loom bar 22, and an arm (not shown) which is affixed to the control box 14 of the optical sensing head 26. The optical sensing head 26, shown with its front cover removed, is centrally positioned above the shuttle box 20 and therefore, centrally located above the shuttle 34 and the bobbin 36 retained therein when the shuttle 34 is boxed.

:Recessedly mounted within the optical sensing head housing 25 are two photoelectric sensing devices (photocells) 28 and 30 and a light source (lamp) 32. Photocell 28 is a dual photocell having two sensing elements 27 and 29 included therein. Electrical connections between the photocells 28 and 30, the lamp 32 and the control box 14 are made through a channel 33 provided in the arm and sensing head 26. The lamp 32 is mounted in a socket 35 which is affixed to the sensing head housing 25.

The preferred embodiment of the present invention utilizes a single casting which includes a control box 14,

an arm and mounting bracket as described earlier. It is to be understood that a multi-section housing assembly may also be used to obtain the same result.

The bobbin 36 shown in FIGS. 1 and 2 is in a shuttle 34 in its relative position with respect to an optical sensing head 26, when the shuttle 34 is stopped by a stop 38 and boxed in a shuttle box 20 of a fly-shuttle loom, not shown. The shuttle 34 is normally provided with an opening through which the bobbin is visible and may be viewed from the optical sensing head 26. The opening in the shuttle always occurs in the same position when the shuttle is boxed.

The light rays emanating from a lamp 32 are focused by a lens 44 at a point 46 above the surface 48 of the bobbin 36. This results in an oval-shaped light projection 48 on the surface 52 of the bobbin 36 approximately 1% inch long. The bobbin 36, in thepreferred embodiment, having a relatively smooth (specular) surface reflects sufficient light to photocell 28 to change its impedance but reflects relatively little light to photocell 30 and does not significantly change its impedance. If yarn threads 50 (weft material) are on the bobbin in the surface ares'52, then the surface of the illuminated area will no longer be smooth and the light rays 53 (FIG. 1) will be reflected at a multiplicity of angles because of the diffuse reflecting characteristics of the weft material 50. Relatively equal amounts of light will reach photocells 28 and 30 thereby changing their impedances approximately the same amount. The importance of the impedance changes of the photocells will become apparent when the operation of the detector is described in conjunction with FIG. 3.

Although in the preferred embodiment the bobbin is considered to have a specularly reflecting surface and the weft material is described as having a diffuse reflecting surface, the principles of the present invention may be utilized with reverse characteristics of the bobbin and weft material. Modification to the circuits shown in FIG. 3 may be made by persons knowledgeable in the art to accept this altered criteria. In accordance with the principles of this invention, it is only necessary that the reflecting surface of the bobbin is different than the reflecting surface of the weft material.

It is to be noted at this time that the sensing of the weft on the bobbin is performed when the lay bar is in its most forward position, and that since the photocells 28 and 30 are recessed within the optical sensing head 26 they substantially receive light rays only when the bobbin surface is in a specified position plus or minus small tolerance variations. This avoids a possible erroneous signal which might be obtained from the surface of the lay bar which passes the detecting sensors before the bobbin comes to the most forward position.

The present preferred embodiment of the invention provides for a mechanical adjustment of the photocells 28 and 30 by mounting them on slide brackets 37 and 39, respectively. The slide brackets 37 and 39 are mounted to the housing 25 of the optical sensing head 26 by means of shoulder screws 41 which permits the photocells 28 and 30 to be adjusted in position within the openings 43 and 45 of tubular sensor shields 47 and 49, respectively. The sensor shields 47 and 49 are affixed to the housing 25 by screws 51.

Although the distance of the photocells 28 and 30 from the surface of the bobbin is adjusted with the aid of slide brackets 37 and 39 to optimize the light reaching the respective photocells, large bursts of light occuring because of reflections from the lay bar itself or from sunlight entering the room in a random matter, would still, cause ejection of the bobbin before the weft was completely exhausted. Early solutions to this problem included the use of a third photocell or a mechanical interlock toprevent erroneous ejections of the bobbin. This insured that the most forward portion of the lay bar was sensed and that the shuttle was boxed before permitting the activation of the sensor at a particular time in the loom cycle. However, this technique did not prove successful, since continuous adjustment of a mechanical interlock was required. When a photoelectric sensor was used to determine the most forward position of the lay bar, lint or dirt carried in the atmosphere would soon cover the photoelectric sensor, thereby providing erroneous results.

The present invention overcomes problems encountered in prior photoelectric sensing systems by utilizing a dual photoelectric sensor 28 which has incorporated therein two separate sensors 27 and 29. Thus, the light entering the opening 43 falls equally on photocells 27 and 29, thereby changing their impedance accordingly. A critical adjustment or mechanical alignment of the lay bar is no longer required. The location of the photocells 27 and 29 remove them from the generally lint laden atmosphere insuring minimum interference with their proper operation. The additional photocell 29 serves to function as the required interlock, but more accurately depends upon the position of the bobbin and the amount of thread thereon, rather than just the position of the lay bar. This photocell activates the electronic circuitry only during the period that it senses the light, or lack of it, reflecting from the bobbin itself and activats the electronic circuitry only during a very small portion of the loom cycle, thereby reducing the possibility of sudden changes of ambient light from causing the bobbin to be ejected prior to its being empty of weft thread.

Incorporated within the control box 14 of the improved photoelectric weft detector 10 are the components, shown schematically in FIG. 3, that provide the DC voltage which in turn energizes a triggering solenoid 60 that ejects the bobbin and starts the bobbin replacement cycle of the loom in a conventional manner.

A source of power foroperation of the preferred embodiment of the photoelectric weft detector 10 is the existing loom power supply 62 shown in FIG. 3, which is normally 50-60 Hz at 10 to 15 volts. The 50-60 Hz is rectified by a full wave bridge circuit 63 including diodes 64, 66, 68, and 70. A fuse 72 is also included for overload and short circuit protection.

The unfiltered DC voltage obtained from bridge circuit is coupled to a regulated lamp supply circuit 73, which contains a resistor 74 and a Zener diode 76 to limit the voltage at a peak value of approximately 9.1 volts. For consistent sensing, the light intensity is maintained at a constant value by regulating the voltage to a light source 32, which in the preferred embodiment, is a GB. 253 instrument type lamp operating at 2.5 volts and 0.35 amperes. Another voltage protection circuit for the lamp 32 is also provided and will be described hereinafter.

A voltage divider composed of resistors 78, 80 and 82 is connected across the rectified DC voltage source lines 83 and 85 and provides a reference voltage for the gate electrode 86 of the programmable unijunction transistor (PUT) 88. Resistor 84 is connected in parallel with resistor 80 and is selected to adjust the voltage appearing at the gate electrode 86 of the PUT and is chosen to provide 2.5 volts rms across the light or lamp source 32.

At the start of a cycle a capacitor 90, connected from the anode electrode 92 of the PUT 88 to line 85, starts to charge through resistors 74 and 94 causing the voltage at the anode electrode 92 to increase at a rate determined by the RC time constant [(R R X C However, the voltage at the gate electrode 86 of the PUT rises in accordance with the line voltage. PUT 88 is unable to fire until some time after 90 of a line frequency cycle has elapsed since the anode electrode 92 cannot become more positive than the gate electrode 86 until the DC supply voltage decreases (between 90 and 180 of the line cycle). The anode electrode 92 tends to remain at a more positive voltage than the gate electrode 86 because capacitor 90 holds its voltage while the gate electrode voltage decreases with the line voltage.

At a point in the cycle between 90 and 180 when the anode electrode voltage exceeds the gate electrode voltage by approximately 0.5 volts the PUT 88 fires (becomes low resistance between its anode electrode 92 and its cathode electrode 96) thereby discharging capacitor 90 into cathode resistor 98 and the gatecathode junction of silicon controled rectifier (SCR) 100.

The anode and cathode electrodes of SCR 100 are connected in series with a light source 32 and a resistor 95 across a source of DC voltage (lines 83 and 85). When capacitor 90 discharges into the gate-cathode junction of SCR 100 it cause SCR 100 to fire, thereby, causing the DC source voltage to appear across the light source 32. Resistor 84 is chosen to set the firing point of the PUT at a specified portion of each cycle to obtain 2.5 volts rms across the light source 32 as mentioned earlier.

When the line voltage decreases, the voltage at the gate electrode 86 of the PUT 88 correspondingly reduces, therefore, the anode electrode 92 of the PUT 88 can become more positive than the gate electrode 86 earlier in the cycle, thus increasing the conduction angle of the SCR 100. When the line voltage increases, the gate electrode voltage increases, thereby making the anode electrode become more positive than the gate electrode at a later time in the cycle and decreasing the condition time of the SCR. This circuit, therefore, provides a substantially constant voltage across the light source 32 for a varying input voltage source. The second half of the line voltage cycle between 180 and 360 performs just as the first half previously described since the AC is full wave rectified. The SCR 100 resets (becomes a high impedance) each time the voltage goes to zero and the SCR has less than holding current flowing through it. The PUT88 returns to its non-conducting state at substantially the same time since capacitor 90 is essentially completely discharged and starts its charging cycle as soon as the zero voltage portion of the cycle is passed.

Noise pulses (sudden reductions in voltage caused by the power SCR 104 firing) can cause premature firing of PUT 88 resulting in voltage surges across and possible burn out of light source 32. In addition an overvoltage circuit is provided to protect the voltage appearing across the lamp 32. This circuit includes SCR 9]; Zener diode 93; and resistors 95 and 97. The anode electrode of SCR 91 is connected to one side of lamp 32 and the cathode electrode of sCR 91 is connected to the other side of lamp 32. The resistor 95 is serially connected between the anode electrode of SCR 91 and the cathode electrode of SCR 100, the anode electrode of SCR being connected to line 83, which is the source of DC voltage mentioned earlier. If for any reason the voltage appearing across lamp 32 should exceed the desired amount it would at the same time increase the voltage appearing at the cathode electrode of sCR 100. The Zener diode 93, connected from the cathode electrode of SCR 100 to the gate electrode of SCR 91 would be caused to conduct current through resistor 97 and the gate-cathode junction of SCR 91 to line 85, thereby, causing SCR 91 to fire (become a low impedance). Since SCR 91 is in parallel with lamp 32 it would effectively absorb any increased voltage by increasing the current flow through resistor 95. The SCR 91 would reset as the line voltage went through zero.

The full wave rectified DC voltage is also coupled to the DC regulator circuitry 108, via diode 1 10 and resistor 114. A filter capacitor 1 16 is coupled from the positive voltage line 118 to the reference (negative) line 126. Diode functions to isolate the control circuitry from the regulated lamp circuit 73 used to feed the light source 32. Resistor 114 is a current surge limiter for the capacitor 116..

The DC voltage, in the preferred embodiment is regulated at approximately 9.1 volts DC, in a conventional power supply circuit comprising, a transistor 119, a resistor 120, a capacitor 121, and a Zener diode 122. The regulated DC output voltage appearing between lines 124 (positive) and 1 26 (negative) is coupled to the photocells 28 (27 and 29) and 30; a comparator circuit 134; an inhibit circuit 135; and a multivibrator circuit 136.

Resistors 138 and 140 are serially connected across the filtered and regulated DC voltage appearing across lines 124 and 126 and function as a voltage divider to maintain the voltage at the anode electrode of PUT 142 at a predetermined value (50 percent of the voltage appearing across lines 124 and 126) should the photocells 28 and 30 receive smalldifferences of light due to ambient light changes or should the photocells open up or be removed for any reason. The voltage appearing at the anode electrode 'of PUT 142, therefore, depends upon the resistance valuesof photocells 27 and 30. Photocell 29 is connected in series with resistor 137 across lines 124 and 126. The junction of photocell 29 and resistor 137 is coupled, via a capacitor 139, to the input terminal 141 of Schmitt trigger 143. In the preferred embodiment of the invention, Schmitt trigger 143 is an integrated circuit module purchased from the Amperex Corporation Part. No. TAA 560. Resistors 132 and 133 are serially connected across the DC voltage lines 124 and 126. The junction of resistors 132 and 133 is connected to the input terminal 141 of Schmitt trigger 143 to set the DC operating voltage. Resistors 145 and 147 are also serially connected across the DC voltage lines 124 and 126. The junction of resistors 145 and 147 is coupled to the B+ terminal 151 of Schmitt trigger 143 and'determines the operating voltage of the module. Diode 149 is coupled between terminal 141 and terminal 151 of the Schmitt trigger 143 thereby prohibiting any input signal from exceeding the B+ voltage which would damage the Schmitt trigger. The output terminal 157 of Schmitt trigger 143 is coupled to the junction of resistors 138 and 140.

When a light source, such as a lamp 32, illuminates photocells 27, 29 or 30 they change to a relatively low resistance value. The voltage at the anode electrode of PUT 142 is unable to build up beyond the threshold value since the output terminal 157 of the Schmitt trigger 143 provides a low impedance to line 126 via the return terminal 161 of Schmitt trigger 143. When the light beam strikes photocell 29 it becomes a low resistance thereby changing the value of the voltage appearing at the junction of photocell 29 and resistor 137. This voltage is coupled across capacitor 139 to the input terminal 141 of the Schmitt trigger 143 thereby changing its output state. The change in the output state of the Schmitt trigger 143 causes the impedance between terminals 157 and 161 to become relatively large, thereby permitting the voltage to build up across resistor 140 in a manner dictated by the ratio of resistances 138 and 140.

The impedance ratio of photocells 27 and 30 now govern the voltage appearing at the anode electrode PUT 142. A capacitor 144 is coupled between the anode electrode of PUT 142 to the gating electrode of PUT 142 to reduce extraneous noise pulses thereby eliminating the misfiring of PUT 142.

Resistors 146 and 148 are connected across lines 124 and 126 and function as a voltage divider to provide a reference voltage to the gate electrode of PUT 142. Variable resistor 150 is connected in parallel with resistor 146 and provides a means for adjusting the threshold voltage or firing point of PUT 142 since the junction of resistors 146 and 148 is coupled to the gate electrode of PUT 142. Connected between the cathode electrode of PUT 142 and line 126 is a resistor 152 which functions to limit the anode-to-cathode current of PUT 142 to a value below the valley current value when it fires. The current pulse that occurs in resistor 152 generates a voltage across resistor 152 which is coupled, via capacitor 153, to aninverting' amplifier transistor stage comprised of a transistor 154, resistors 156 and 158, and'output coupling capacitor 160. Capacitor 160 couples the pulse to a conventional monostable multivibrator circuit comprised of transistors 162 and 164; resistors 166, 168, 170, and 172; and capacitor 174. Transistor 162 is normally off and transistor 164 is normally on. The collector electrode of transistor 164 is coupled, via diode 178, to the gate electrode of SCR 104. Since transistor 164 is normally on, no voltage is available at the gate electrode of SCR 104 to turn it on or fire it, so it remains in its nonconducting state. Resistor 180 is connected from the gate electrode to the cathode electrode of SCR 104 and functions to provide an external DC current path between the gate and cathode electrodes and reduces the possibility of misfiring of SCR 104 due to noise pulses. A diode 182 which is connected in series with SCR 104 and solenoid 60 across the full wave bridge circuit 63 helps to insure that SCR 104 turns off after firing, when the rectified full wave voltage reduces to zero. Free wheeling diode 183 is connected across solenoid 60 and functions to maintain current flow inthe solenoid for a short time after the SCR 104 turns off.

In order to reduce the sensitivity of the sensitive electronic circuitry included in the improved photoelectric weft detector it is necessary to include transient bypass capacitors. These capacitors are installed at various positions in thecircuitry to reduce erroneous bobbin replacement to a negligible level. A pair of these transient suppression capacitors 184 and 186 are connected in series across solenoid 60. The junction of these capacitors is connected to loom ground. Another pair of capacitors 188 and 190 are serially connected across lamp 32. The junction of the capacitors is also connected to the loom ground. Capacitor 192, connected from one side of fuse 72 to the loom ground also surpresses transients appearing on the input line.

The operation of the improved circuit is explained as follows. A shuttle containing a bobbin which has weft material thereon with a diffuse reflecting characteristic reflects light rays to photocells 27, 29 and 30. Since all the photocells sense nearly equal light their impedances are nearly the same and the voltage appearing at anode electrode of PUT 142 is essentially one half of the voltage appearing across the lines 124 and 126. It is to be noted that changes in the ambient light level or changes in the intensity of the light source will effect all the photocells equally so that the voltage at the anode electrode of PUT 142 will not change thereby. As mentioned earlier, the voltage at the anode of PUT 142 is governed in addition to the impedance appearing across terminals 157 and 161 of Schmitt trigger 143, by resistors 138 and 140, and photocells 27 and 30. Since the impedance across terminals 157 and 161 is normally low, resistance is effectively shorted out, thereby prohitibing the voltage at the anode of PUT 142 from reaching the firing level. When the Schmitt trigger changes its state causing the impedance across terminals 157 and 161 to increase to a value relatively large when compared to the value of resistance 140 the voltage appearing at the anode electrode of PUT 142 is then governed by the relative impedance ratios of photocells 27 and 30.

The voltage at the anode of PUT 142, (V is given by:

and is a function only of the ratio of the resistance of photocells 27 and 30.

When the weft material is exhausted from the specular reflecting surface of the bobbin it permits more light rays to reach photocells 27 and 29 than reaches the photocell 30. Photocells 27 and 29 sense the additional light and change to a low resistant state. The magnitude of their resistance is a function of the amount of light they receive. The initial light sensed by a photocell causes its resistance to drop fairly rapidly and then recover somewhat to a resistance value slightly larger than its initial resistance when it first sensed light but much lower than its resistance when it is sensing only light reflected from the diffuse reflecting surface. The lower resistance of photocell 29 causes Schmitt trigger 143 to change states. Since the ratio of resistance of photocell 27 to 30 has gone down, the voltage at the anode electrode of PUT 142 increases. When the light is sufficient to cause the anode electrode voltage of PUT 142 to exceedthe value previously set on the gate electrode of PUT 142 it will fire, thereby generating a positive pulse across resistor 152, which is inverted and amplified by transistor 154.

The negative pulse at the collector of transistor 154 is coupled, via capacitors 160 and 174, to the base electrode of transistor 164 which is driven to an off condition. This permits the DC voltage on line 124 to be coupled through resistor 170 and diode 178 to the gate electrode of sCR 104 thereby firing it. In this condition the monostable multivibrator 136 is in its unstable state and will remain so for a period which is determined by the time constant of resistor 168 and capacitor 174 (R168 X 114)- When SCR 104 fires, almost all of the voltage across the full wave bridge circuit 63 appears across solenoid 60 energizing it. Solenoid 60 remains in this condition as long as SCR 104 conducts.

A mechanical linkage (not shown) is activated by the energizing of the solenoid 60 which in turn causes the bobbin change mechanism (also not shown) to latch up and operate in a conventional manner.

In a preferred embodiment of the invention the time constant of the monostable multivibrator 136 is approximately 75 milliseconds. At the expiration of the time constant the capacitor 174 is charged up to almost the full DC voltage between lines 124 and 126. The positive voltage on the capacitor 174 turns on transistor 164 again which in turn turns off transistor 162. Thus, the monostable multivibrator 136 returns to its normal stage and is ready for the next cycle. With the positive voltage withdrawn from the gate of SCR 104 it will turn off as soon as the current flow through it reduces to below its holding value. The current through SCR 104 reduces to substantially zero when the voltage from the full wave bridge circuit 63 reduces to zero each half cycle, thereby releasing solenoid 60 until the next time the weft material is exhausted.

Hereinbefore has been disclosed a new and improved weft detector which provides for adjusting the distance of the photoelectric cells from the reflecting surface to maximize the useable light available and further includes an inhibit or interlock circuit whereby the electronic circuitry is only activiated at the same time that the reflected light reaches the sensing photocells.

Having thus set forth the nature of thisinvention, what is claimed herein is:

1. An improved system for detecting in a specified area the presence or absence of material having a first reflecting surface comprising:

a. means having a second reflecting surface for supporting said material;

b. means for providing light to said specified area;

c. first means arranged to sense said light reflected from said specified area in the presence or absence of said material, said first means having an impedance proportional to the amount of light sensed and being provided with means for adjusting the distance between said specified area and said first means to increase its sensitivity only to light reflected therefrom;

d. second means arranged only to sense light reflected from said specified areain the presence of said material, said second means having an impedance proportional to the amount of light sensed and being provided with means for adjusting the distance between said specified area and said second means to increase its sensitivity only to light reflected therefrom;

e. utilization means;

f. third means coupled between said first and second means and said utilization means for activating said utilization means in accordance with a predetermined ratio of impedance of said first and second means responsively to the presence or absence of same material; and

g. fourth means coupled to said third means and mounted in close proximity to said first means, for activating said third means upon sensing light reflected by the absence of said material from said specified area.

2. An improved system for detecting in a specified area the presence or absence of material having a diffuse reflecting surface comprising;

a. means having a specular reflecting surface for supporting said material;

b. means for providing light to said specified area;

c. first means arranged to sense said specular and diffuse light reflected from said specified area in the presence or absence of said material, said first means having an impedance proportional to the amount of light sensed and being provided with means for adjusting the distance between said specified area and said first means toincrease its sensitivity only to light reflected therefrom;

d. second means arranged only to sense diffuse reflected light from said surface area, said second means having an impedance proportional to the amount of light sensed and being provided with means for adjusting the distance between said specified area and said second means to increase its sensitivity only to light reflected therefrom;

e. utilization means;

f. third means coupled between said first and second means and said utilization means for activating said utilization means in accordance with a predetermined ratio of impedance of said first and second means responsively to the presence or absence of said material; and

g. fourth means coupled to said third means and mounted in close proximity to said first means for activating said third means upon sensing specular light being reflected from said specified area in the absence of said material.

3. An improved system for detecting in a specified area the presence or absence of material having a specular reflecting surface comprising:

a. means having a diffuse reflecting surface for supporting said material;

b. means for providing light to said specified area;

c. first means arranged to sense said specular and diffuse light reflected from said specified area in the presence or absence of said material, said first means having an impedance proportional to the amount of light sensed and being provided with means for adjusting the distance between said specified area and said first means to increase its sensitivity only to light reflected therefrom;

d. second means arranged only to sense diffuse reflected light from said surface area, said second means having an impedance proportional to the amount of light sensed and being provided with means for adjusting the distance between said specified area and said second means to increase its sensitivity only to light reflected therefrom;

e. utilization means;

f. third means coupled between said first and second means and said utilization means for activating said utilization means in accordance with a predetermined ratio of impedance of said first and second means responsively to the presence or absence of said material; and

g. fourth means coupled to said third means and mounted in close proximity to said first means for activating said third means upon sensing a lack of specular light reflected from said specified area in the absence of said material.

4. A loom weft detecting system for detecting the exhaustion of weft having a diffuse reflecting surface from a specified area comprising:

a. a bobbin for supporting said weft, said bobbin having a specular reflecting surface relative to that of the weft;

b. means illuminating said specified area by a beam of light incident to said bobbin surface at an angle to the normal to said bobbin surface;

c. a first photocell for receiving specular and diffuse light from said surface area and being provided with means for adjusting the distance between said specified area and said first photocell to increase its sensitivity only to light reflected therefrom;

d. a second photocell for receiving diffuse reflected light from said surface area being positioned closely adjacent said incident beam of light and at a distance from said surface substantially equal to the distance said first photocell is from said surface and being provided with means for adjusting the distance between said specified area and said sec ond photocell to increase its sensitivity only to light reflected therefrom;

e. means for deriving a DC voltage related to the ratio of the resistance of said first and second photocells;

f. means establishing a threshold voltage, said threshold voltage being intermediate in value between the values of the voltages established by the photocells in the presence and in the absence of said weft on the surface of the illuminated area;

g. means responsive to the derived DC voltage value exceeding said threshold voltage for actuating a solenoid when said weft is exhausted from said bobbin; and

h. a third photocell coupled to said DC voltage deriving means for receiving specular and diffuse light from said surface area being afiixed proximate said first photocell, said third photocell inhibiting said means for deriving a DC voltage until it senses specular light being reflected from said specified area.

5. A loom weft detecting system for detecting the exhaustion of weft having a specular reflecting surface from a specified area comprising:

a. a bobbin for supporting said weft, said bobbin having a diffuse reflecting surface relative to that of the weft;

b. means illuminating said specified area by a beam of light incident to said bobbin surface at an angle to the normal to said bobbin surface;

c. a first photocell for receiving specular and diffuse light from said surface area and being provided with means for adjusting the distance between said specified area and said first photocell to increase its sensitivity only to light reflected therefrom;

d. a second photocell for receiving diffuse reflected light from said surface area being positioned closely adjacent said incident beam of light and at a distance from said surface substantially equal to the distance said first photocell is from said surface and being provided with means for adjusting the distance between said specified area and said second photocell to increase its sensitivity only to light reflected therefrom;

e. means for driving a DC voltage related to the ratio of the resistance of said first and second photocells;

f. means establishing a threshold voltage, said threshold voltage being intermediate in value between the values of the voltages established by the photocells in the presence and in the absence of said weft on the surface of the illuminated area;

g. means responsive to the derived DC voltage value exceeding said threshold voltage for actuating a solenoid when said weft is exhausted from said bobbin; and

h. a third photocell coupled to said DC voltage deriving means for receiving specular and diffuse light from said surface area being affixed proximate said first photocell, said third photocell inhibiting said means for deriving a DC voltage until it senses the lack of specular light being reflected from said specified area.

I' F i 

1. An improved system for detecting in a specified area the presence or absence of material having a first reflecting surface comprising: a. means having a second reflecting surface for supporting said material; b. means for providing light to said specified area; c. first means arranged to sense said light reflected from said specified area in the presence or absence of said material, said first means having an impedance proportional to the amount of light sensed and being provided with means for adjusting tHe distance between said specified area and said first means to increase its sensitivity only to light reflected therefrom; d. second means arranged only to sense light reflected from said specified area in the presence of said material, said second means having an impedance proportional to the amount of light sensed and being provided with means for adjusting the distance between said specified area and said second means to increase its sensitivity only to light reflected therefrom; e. utilization means; f. third means coupled between said first and second means and said utilization means for activating said utilization means in accordance with a predetermined ratio of impedance of said first and second means responsively to the presence or absence of same material; and g. fourth means coupled to said third means and mounted in close proximity to said first means, for activating said third means upon sensing light reflected by the absence of said material from said specified area.
 2. An improved system for detecting in a specified area the presence or absence of material having a diffuse reflecting surface comprising; a. means having a specular reflecting surface for supporting said material; b. means for providing light to said specified area; c. first means arranged to sense said specular and diffuse light reflected from said specified area in the presence or absence of said material, said first means having an impedance proportional to the amount of light sensed and being provided with means for adjusting the distance between said specified area and said first means to increase its sensitivity only to light reflected therefrom; d. second means arranged only to sense diffuse reflected light from said surface area, said second means having an impedance proportional to the amount of light sensed and being provided with means for adjusting the distance between said specified area and said second means to increase its sensitivity only to light reflected therefrom; e. utilization means; f. third means coupled between said first and second means and said utilization means for activating said utilization means in accordance with a predetermined ratio of impedance of said first and second means responsively to the presence or absence of said material; and g. fourth means coupled to said third means and mounted in close proximity to said first means for activating said third means upon sensing specular light being reflected from said specified area in the absence of said material.
 3. An improved system for detecting in a specified area the presence or absence of material having a specular reflecting surface comprising: a. means having a diffuse reflecting surface for supporting said material; b. means for providing light to said specified area; c. first means arranged to sense said specular and diffuse light reflected from said specified area in the presence or absence of said material, said first means having an impedance proportional to the amount of light sensed and being provided with means for adjusting the distance between said specified area and said first means to increase its sensitivity only to light reflected therefrom; d. second means arranged only to sense diffuse reflected light from said surface area, said second means having an impedance proportional to the amount of light sensed and being provided with means for adjusting the distance between said specified area and said second means to increase its sensitivity only to light reflected therefrom; e. utilization means; f. third means coupled between said first and second means and said utilization means for activating said utilization means in accordance with a predetermined ratio of impedance of said first and second means responsively to the presence or absence of said material; and g. fourth means coupled to said third means and mounted in close proximity to said first means for activating said third means upon sensing a lack of specular light reflected from said specified area in the absence of said material.
 4. A loom weft detecting system for detecting the exhaustion of weft having a diffuse reflecting surface from a specified area comprising: a. a bobbin for supporting said weft, said bobbin having a specular reflecting surface relative to that of the weft; b. means illuminating said specified area by a beam of light incident to said bobbin surface at an angle to the normal to said bobbin surface; c. a first photocell for receiving specular and diffuse light from said surface area and being provided with means for adjusting the distance between said specified area and said first photocell to increase its sensitivity only to light reflected therefrom; d. a second photocell for receiving diffuse reflected light from said surface area being positioned closely adjacent said incident beam of light and at a distance from said surface substantially equal to the distance said first photocell is from said surface and being provided with means for adjusting the distance between said specified area and said second photocell to increase its sensitivity only to light reflected therefrom; e. means for deriving a DC voltage related to the ratio of the resistance of said first and second photocells; f. means establishing a threshold voltage, said threshold voltage being intermediate in value between the values of the voltages established by the photocells in the presence and in the absence of said weft on the surface of the illuminated area; g. means responsive to the derived DC voltage value exceeding said threshold voltage for actuating a solenoid when said weft is exhausted from said bobbin; and h. a third photocell coupled to said DC voltage deriving means for receiving specular and diffuse light from said surface area being affixed proximate said first photocell, said third photocell inhibiting said means for deriving a DC voltage until it senses specular light being reflected from said specified area.
 5. A loom weft detecting system for detecting the exhaustion of weft having a specular reflecting surface from a specified area comprising: a. a bobbin for supporting said weft, said bobbin having a diffuse reflecting surface relative to that of the weft; b. means illuminating said specified area by a beam of light incident to said bobbin surface at an angle to the normal to said bobbin surface; c. a first photocell for receiving specular and diffuse light from said surface area and being provided with means for adjusting the distance between said specified area and said first photocell to increase its sensitivity only to light reflected therefrom; d. a second photocell for receiving diffuse reflected light from said surface area being positioned closely adjacent said incident beam of light and at a distance from said surface substantially equal to the distance said first photocell is from said surface and being provided with means for adjusting the distance between said specified area and said second photocell to increase its sensitivity only to light reflected therefrom; e. means for driving a DC voltage related to the ratio of the resistance of said first and second photocells; f. means establishing a threshold voltage, said threshold voltage being intermediate in value between the values of the voltages established by the photocells in the presence and in the absence of said weft on the surface of the illuminated area; g. means responsive to the derived DC voltage value exceeding said threshold voltage for actuating a solenoid when said weft is exhausted from said bobbin; and h. a third photocell coupled to said DC voltage deriving means for receiving specular and diffuse light from said surface area being affixed proximate said first photocell, said third photocell inhibiting said means for deriving a DC voltage until it senses the lack of specular light being reflected from said specified arEa. 